-=UPDATE=-
I've had a bit of interest already, and I'm asking interested parties to pmail me with offers that they think are reasonable price-differences between 1260 and 603e+.
In terms of the practicalities of the trade, I'm thinking the best thing could be for me to sell my card for an agreed price, taking payment via PayPal (and posting with registered/insurance) on the understanding that the other party sells their 1260 for an agreed lower price to me, also to be paid via PayPal etc.
Of course if people have other solutions, I'm happy to hear them:)